Abstract
The production of secondary metabolites with antibiotic properties is a common characteristic to entomopathogenic bacteria Xenorhabdus spp. These metabolites not only have diverse chemical structures but also have a wide range of bioactivities of medicinal and agricultural interests. Culture variables are critical to the production of secondary metabolites of microorganisms. Manipulating culture process variables can promote secondary metabolite biosynthesis and thus facilitate the discovery of novel natural products. This work was conducted to evaluate the effects of five process variables (initial pH, medium volume, rotary speed, temperature, and inoculation volume) on the antibiotic production of Xenorhabdus bovienii YL002 using response surface methodology. A 25–1 factorial central composite design was chosen to determine the combined effects of the five variables, and to design a minimum number of experiments. The experimental and predicted antibiotic activity of X. bovienii YL002 was in close agreement. Statistical analysis of the results showed that initial pH, medium volume, rotary speed and temperature had a significant effect (P<0.05) on the antibiotic production of X. bovienii YL002 at their individual level; medium volume and rotary speed showed a significant effect at a combined level and was most significant at an individual level. The maximum antibiotic activity (287.5 U/mL) was achieved at the initial pH of 8.24, medium volume of 54 mL in 250 mL flask, rotary speed of 208 rpm, temperature of 32.0°C and inoculation volume of 13.8%. After optimization, the antibiotic activity was improved by 23.02% as compared with that of unoptimized conditions.
Highlights
Xenorhabdus is a unique genus of bacteria symbiotically associated with entomopathogenic nematode belonging to genus Steinernema
analysis of variance (ANOVA) and Model Fitting In order to evaluate the relationship between response and independent variables and to determine the maximum antibiotic activity production corresponding to the optimal levels of initial pH (X1), medium volume (X2, Medium volume (mL)), rotary speed (X3, rpm), temperature (X4, uC) and inoculation volume (X5, %), a secondorder polynomial model was proposed to calculate the optimal levels of these variables
We focused on the optimization of the culture conditions for the antibiotic production of X. bovienii YL002 through factorial design using response surface analysis
Summary
Xenorhabdus is a unique genus of bacteria symbiotically associated with entomopathogenic nematode belonging to genus Steinernema. The bacterial symbionts are believed to prevent putrefaction of the insect cadaver and establish conditions that favor the development of both the nematode and bacterial symbionts. The antimicrobial nature of metabolites produced by Xenorhabdus spp. is known, and several compounds with antibiotic activity have been isolated and identified. These include indoles [4], xenorhabdins [5], xenocoumacin [6], nematophin [7], benzylineacetone [8], xenortides and xenematide [9] and cyclolipopeptide [10]. These metabolites have diverse chemical structures, and have a wide range of bioactivities of medicinal and agricultural interests such as antibiotic, antimycotic, insecticidal, nematicidal, antiulcer, antineoplastic and antiviral
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